This invention relates to a precision cutting of discrete devices such as, for example, ink jet printheads and, more particularly, to a resinold/diamond dicing blade used for said precision cutting and a method of making the blade.
There are many prior art discrete devices which are formed as a plurality of substrates integrally formed in a wafer or the like in which require intermediate cuts and/or separation into individual subunits is a last step in the fabrication process. Examples of such discrete devices are ink jet printheads, magnetic heads, and semiconductor sensor devices. Most, but not all, of the devices are formed in silicon-based wafers. A preferred technique for separating the sub-units is to saw through the wafer in a procedure referred to as "dicing". The device used to perform the cutting is referred to as a dicing blade or dicing saw. For cutting operations requiring high precision (.+-.0.5 micron) resinold/diamond blades have been preferred, especially in the production of thermal ink jet printheads, because they form precisely placed, smooth chipless cuts. Prior art resinoid/diamond blades have been typically constructed of a resin-diamond blend. For example, a resinold/diamond blade is disclosed in U.S. Pat. No. 4,878,992 which is constructed of a relatively hard, dense resin bonded material and a 60 to 90% concentration of natural or synthetic diamonds. Other resinold/diamond blades and their use are disclosed in U.S. Pat. Nos. 5,160,403, 5,266,528 and 4,851,371.
These prior art resinold/diamond blades still suffer from performance variability manifested in the asymmetric wear of the blade periphery and shortened blade life due to chipping caused by the forces generated when pieces of silicon or diamond particles loosened from the dicing blade become jammed between the rotating dicing blade and the silicon wafers being cut. The use of natural or synthetic diamonds also adds to the expense.
It is therefore one object of the present invention to provide a resinold dicing blade which produces consistent precision cuts with reduced chipping. It is a further object to provide a resinold blade with increased life. It is another object to provide a resinold/diamond blade which is less expensive than prior art blades without sacrificing precision cutting characteristics. It is also an object to provide an electrically conductive blade to enable automatic blade height sensing on the dicing saw. These and other objects, are obtained by constructing a resinold/diamond blade with a plurality of graphite veil layers impregnated with a resin/diamond blend mixture. A layered construction yields a blade with more homogeneous cross-section reducing the potential for asymmetric wear. Further material savings are realized when the diamond filled resin is used only near the periphery of the blade (about 0.100 inch of the outer diameter is actually used). Other advantages of using the impregnated graphite layer are: enhanced design freedom in use of larger grit sizes for inner layer for faster cutting and finer sizes on the outside. Graphite is electrically conductive enabling ongoing blade height checks during the sawing sequence, e.g., monitoring wear, blade life. Also, graphite has a high modulus of elasticity and therefore helps to provide blade stiffness in cross-section.